The capacity of a current flowing through a power module has increased. Accordingly, a lead electrode that is an external terminal needs to have a large area or a large area in which the lead electrode is joined to an external electrode so as not to generate heat. Such a configuration unfortunately involves a large package of a product as a whole. The power module increasingly needs to have high performance, have high endurance, and be miniaturized; hence the large package of the product as a whole resulting from the large capacity of the current is incompatible with a need for a miniaturized product.
In a conventional semiconductor device, heat generated in a semiconductor element is dissipated through solder, a heat spreader, an insulating layer, and a heat dissipation material, all of which are disposed below the semiconductor element. On the other hand, the external terminal or the lead electrode connected above the semiconductor element through solder includes no heat dissipation mechanism. Hence, heat generated in the semiconductor element or heat generated in the lead electrode itself causes the lead electrode to have a high temperature. The lead electrode is expected to have a higher temperature as the capacity of the current increases. To prevent the heat generation of the lead electrode, the lead electrode needs to have a large width or a large thickness.
Patent document 1 discloses one example of a technique for improving the heat dissipation capability of the semiconductor element and the heat dissipation capability of the lead electrode. In this technique, an insulating substrate is disposed on an upper surface of the external terminal connected to the semiconductor element, and is exposed to the outside of a module; this helps heat to be dissipated from an upper surface of the semiconductor element, thereby preventing the heat generation of the external terminal.